Unable to back up Office 365 user emails.
Your administrative user needs to implement the User Impersonation in Microsoft's Exchange Online. Follow the steps below (or see attached document) for instructions:
Configuring Exchange Online Impersonation
1. Log in as administrator at https://portal.microsoftonline.com/
2. Go to the ‘Exchange” Admin section:
3. In ‘Exchange admin center’ go to the ‘permissions’>’admin roles’ and choose ‘Discovery Management’
4. On the ‘Discovery Management’ screen, the ‘ApplicationImpersonation’ role should be added (+ button), and admin should be a member. See the next steps for instructions about setting up the role and member.
5. Adding the ‘ApplicationImpersonation’ role:
6. Adding ‘admin’ as a member: